Systems for determining the location and content of structures and/or organs in living bodies by detecting X-ray shadow of the body or by detecting high speed particles emanating from regions of the body which have selectively absorbed a radioactive compound require substantial exposure of the living body to potentially harmful radiation either by reason of the X-ray source being sufficiently intense and/or of long duration to produce a visual image on a film or from the concentration of the radioactive compound which must be absorbed by the body to emit a sufficient number of high energy particles to produce a useful image. In addition, when X-rays are used, the source of X-rays to produce good images requires that the area of the source be minimized to approach a point source so that when the X-rays were caused, for example, by a high speed electron stream, heating of the target limits the intensity and duration of the X-rays. Attempts to lessen the dosage of radiation to the living body by amplifying the image in the detector region are limited by noise considerations which show up in the final film as snow. In addition, the definition which can be achieved by such a process is limited.
Detection and recording of radiation carrying, as a spatial modulation thereof, image information is well known, such as the exposure of conventional films by light, by X-rays, or by other means; and in such systems, lenses, pinholes or collimators are normally used to form an image of the radiation source on the film or on an observation screen or on an electronic pickup device such as a vidicon camera tube. Such radiation from the object may be, for example, the result of reflection, direct radiation from the body due to its thermal temperature or radioactive content, conversion of incident radiation on the object to a different form of radiation as in the form of a fluorescent object, radiation from a body subject to nuclear energy bombardment, or an object heated by absorption of ligh and reradiation of the thermal energy in the infrared spectrum.
In copending application Ser. No. 360,223 (now U.S. Pat. No. 3,825,757 ), there is disclosed a coding system wherein a spatially distributed pattern of such energy may be coded with respect to a reference code by superimposing a spatially coded reference signal on the radiation pattern, thereby avoiding the need to use a phase coherent source of radiant energy to obtain a holographic form of the radiation pattern since the phase characteristics of the reference signal may be used for the subsequent decoding of the pattern to produce an image.